SHELLS AND SHELL-FISH. PART I. 



sudden ; for it is here we shall insert,, as an intervening 

 form, our sub-genus Ceriphasia (fig. 38.), founded upon 

 certain Ohio shells resembling Ce- 

 rithidea, but whose outer lip is thin 

 and sharp. Unfortunately, we can 

 find no account of the animal, nor 

 are we acquainted with any shells 

 which will connect these with Me- 

 lanopsis on one side, and with Ce- 

 rithidea on the other. Until our 

 path, therefore, is better marked, 

 we must leave their precise situation as doubtful. 

 There are evidently three or four sub-genera un- 

 discovered or uncharacterised, which belong to this 

 genus. One of these, we suspect, will be found in 

 certain small species, figured as Melanopsides by 

 M. Ferussac : their spire is unusually lengthened ; 

 and the whorls are strongly and longitudinally plaited. 

 As our last genus, we introduce Planaxis, the animal 

 of which, having been fully investigated and de- 

 scribed by M. Quoy, proves that their shell must be 

 arranged with the Melaniance. It is difficult to conceive 

 why this eminent malacologist should have introduced 

 it near to Buccinum, when he expressly says that in the 

 structure of the animal it comes close to Melania. If 

 Planaxis was to be arranged from its shell alone, it 

 should be placed next to the Purpurince, since it has 

 the pillar-lip very broad and flattened ; it is, in fact, a 

 Purpura among the Melaniance, and, like them, the 

 eyes of the animal are placed on short peduncles, close 

 to the base of its two long and slender tentacula. Some 

 of these, like the common species, P. subsulcata, has a 

 very short spire; but another, the P. decottata, dis- 

 covered by M. Quoy, has the spire of a Melania, while 

 its name seems to imply that the terminal whorls are 

 deciduous. 



(188.) Having now, as far as possible, analysed this 

 sub-family, a few general remarks may follow. The 

 Melaniance may be viewed as that group of the Tur- 



